各向异性复合材料三维非线性本构行为的实验研究

The objective of the proposed effort is to enable a breakthrough in characterization of composite materials through the development of the first methodology to derive all basic nonlinear stress-strain material constitutive properties in three dimensions, up to the point of material failure, without ad hoc assumptions in the formulation of material properties for structural analysis. The developed methodology will enable accurate and efficient full three-dimensional characterization of nonlinear material properties of composites, using the minimum number of experiments, and will reduce the amount of material testing to understand complex three-dimensional deformation and failure mechanisms in composites. The proposed effort builds on the method for assessing multiple constitutive properties including tensile, compressive, and shear stress-strain relations for composites. The method is based on custom short-beam tests which use digital image correlation (DIC) full-field surface deformation measurements. This method will be expanded to construct initial approximation of the stress-strain relations which will be utilized in much more comprehensive techniques enabling accurate full three-dimensional characterization of nonlinear mechanical properties of composites, using a single specimen configuration and employing synchronized full-field strain measurement in all three principal material planes. In addition, three-dimensional structural analysis will capture internal material structure/microstructure based on 3D measurement and transition of the measured geometric characteristics including manufacturing irregularities into the structural analysis model, to quantify variability in the mechanical properties of composite systems. The impact of the proposed effort includes improved understanding of the complex three-dimensional deformation mechanisms of composite materials and the improved efficiency of measuring their key mechanical propertieswith data from only a few tests. Success of this effort will lead to a breakthrough in the ability to characterize composite materials. As composites begin to play an ever larger role in aircraft structures, the ability to measure their complex properties becomes even more important.

复合材料具有高度各向异性，明显的物理非线性，拉、压弹性模量不同的特点。材料主方向不同应力分量之间存在非线性耦合，且耦合行为在高应力水平时表现突出。针对复合材料复杂的本构行为，本项目旨在发展一套实验方法，通过最少量试验建立正交各向异性复合材料精确的完整三维非线性本构关系，该本构关系能够描述和表征不同失效模式下材料复杂应力条件下的本构行为，材料主方向不同应力分量之间的非线性耦合行为。本构模型的建立过程中不依赖任何材料本构相关的初始假设，通过弹性应变能密度函数推导本构的一般表达形式，利用全场变形测试系统提供完整充分的实测应变数据，采用高精度非线性实体有限元修正技术和优化方法建立材料非线性本构关系。本项目的实施对减少试验，提高结构仿真可靠性，理解复合材料复杂的变形机理，完善强度准则，揭示复合材料缺陷与本构性能的相关性具有重要意义。本项目可在复合材料三维本构关系的表征和实验技术方面形成原创性成果。

复合材料具有高度各向异性，明显的物理非线性，拉、压弹性模量不同的特点。材料主方向不同应力分量之间可能存在非线性耦合，耦合行为在高应力水平时表现突出。采用全场变形测量技术，开展复合材料完整三维本构行为研究对针对复合材料复杂的本构行为，对减少试验，提高结构仿真可靠性，理解复合材料复杂的变形机理，完善强度准则，揭示复合材料缺陷与本构性能的相关性具有重要意义。本项目的实施过程中发展完善了一套针对正交各向异性复合材料的短梁剪切实验方法，实现了通过少量实验建立复合材料完整三维非线性本构关系，该本构关系能够描述和表征不同失效模式下材料复杂应力条件下的本构行为。由于实验方案中结构近似静定结构，有限元模型修正中的应力不依赖材料本构性能参数，因此本构模型的建立过程不依赖任何材料力学性能相关的初始假设，优化过程对材料本构参数初始假设不敏感。研究过程讨论了数字图像相关技术（DIC）中噪声随机误差和重构系统误差对本构参数的影响，提出位移场和应变场重构系统误差对材料本构参数识别具有至关重要的影响，但由于数字图像相关技术中采用子区搜索法，无法确定位移场和应变场的最优重构参数，因此针对采用有限元模型修正或虚场方法识别材料本构行为的研究，采用自适应最优连续的位移场参数（确定最优形函数和单元数量），发展高效高精度全场DIC对该实验方法与虚场法或者有限元模型更新等结合识别本构参数至关重要。该测试方法和流程可推广到其他具有复杂微结构材料的本构行为研究中，通过弹性应变能密度函数推导本构的一般表达形式，利用面内全场变形测试系统提供完整的实测应变数据，采用有限元修正技术和优化方法建立材料非线性本构关系。本项目在复合材料三维本构关系的表征和实验技术方面形成了部分原创性成果，并已经部分推广用于不同体系的复合材料本构参数识别中。